DNA/DNA Hybridization Studies of Marsupials

比较生物学的一个目的是确定模式生物 阐明了进化的一般原理 哺乳动物是 这一点特别有用，因为它们证明了 收敛（重复）进化原理，可用于 测试类似的生态需求引发的命题， 平行进化适应 在这方面 有袋类动物特别重要，因为它们是在 南美洲和澳大利亚的隔离，并开始包括 生态学和解剖学上的“模仿物”更熟悉（胎盘， 或真兽目）哺乳动物。 此外，鉴于大陆的事实 漂移，有袋动物之间的关系本身反映了 大陆的分离和日益分离， 它们发生了，并且在它们之间有明显的趋同相似性。 地理上分离的有袋类动物之间， 真兽亚目;例如，一些美国负鼠是 与澳大利亚有袋动物几乎没有区别， 相似的生活 生物学家长期以来一直在争论， 某些南美和澳大利亚的有袋动物 收敛或代表特殊关系，也许表明 从一个大陆到另一个大陆的额外“入侵”。 到 解决这一争端，并发展有袋动物作为一个模型组， 需要更可靠的家谱。 的问题 获得这样的树是解剖学可以欺骗， 理想情况下，应使用以下方法建立关系， 也可以测量内部或化学特性。 来 从长远来看，遗传物质本身（DNA）似乎以一种 大致恒定的速率;相关物种DNA的比较 因此可以直接测量出物种 与共同祖先的分离 DNA是由两条链组成的，这两条链沿着它们的 化学键的长度。 在这项研究中， 从几个物种中纯化出来，之后， 通过煮沸分离。 一个物种的单链DNA 然后将被允许与它们的杂交或配对， 另一个人的同行。 杂合DNA分子的稳定性 是衡量两个物种之间遗传相似性的指标。 如果测量的热稳定性之间的杂交许多 成对的有袋类物种，进化关系 其中，都可以计算出来。 通过这种方式，可靠的 将构建系统发育树，并与 地理历史和有袋动物生物学的其他特征。

An aim of comparative biology is to identify model organisms that illustrate general principles of evolution. Mammals are especially useful for this purpose because they demonstrate the principle of convergent (repetitive) evolution and can be used to test the proposition that similar ecological demands evoke parallel evolutionary adaptations. In this context, the marsupials are particularly important because they evolved in isolation in South America and Australia, and came to include ecological and anatomical "mimics" of more familiar (placental, or eutherian) mammals. Moreover, given the fact of continental drift, relationships among marsupials themselves reflect the detachment and increasing separation of the continents on which they occur and there are apparently convergent similarities among geographically separated marsupials as well as between these and eutherians; for example, some of the American opossums are almost indistinguishable from Australian marsupials which lead similar lives. Biologists have long argued whether the resemblances of certain South American and Australian marsupials are in fact convergent or represent special relationships, perhaps indicating additional "invasions" of one continent from the other. To settle that dispute, and to develop marsupials as a model group, more reliable genealogical trees are needed. The problem in obtaining such trees is that anatomy can be deceiving, and ideally relationships should be established using methods which measure internal or chemical characteristics as well. Over the long run, the genetic material itself (DNA) seems to change at a roughly constant rate; comparison of the DNAs of related species can therefore give a direct measure of the time of the species' separation from a common ancestor. DNA is made up of two strands held together along their lengths by chemical bonds. In this study, DNA will be extracted and purified from several species, after which the strands will be separated by boiling. Single strands of DNA from one species will then be allowed to hybridize, or pair, with their counterparts from another. The stability of hybrid DNA molecules is a measure of the genetic similarity between the two species. If measurements of the thermal stability of hybrids between many pairs of marsupial species are made, evolutionary relationships among all of them can be calculated. In this manner, a reliable phylogenetic tree will be constructed and correlated with the geographic history and other features of marsupial biology.